In order to keep pace with the demands of data storage in today's information technology, the recording density in disk drives has continued to advance. Current hard disk drive technology uses a magnetic tunneling junction (MTJ) in the read head for reading/sensing purposes. A MTJ includes an antiferromagnetic layer, a synthetic antiferromagnetic structure that serves as a reference layer, a magnetic tunneling barrier, and a free magnetic layer that serves as a storage layer.
An MTJ needs to be processed in such a way that the width of the sensor matches the size of the recorded bit stored in the media which is in the scale of nanometers. As a result, the read-back signal will be subject to a significant level of interference from stray fields coming from nearby bits in the media. Additionally, the high reading speed used in today's technology will significantly raise the noise level.
Also, a hard magnetic film is often used to apply a biasing field to the free layer to stabilize its direction of magnetization. This technique is often called hard bias (HB). There are two major approaches in the existing technology for the side shields namely (1) hard magnetic materials as in the hard bias magnets and (2) permalloy NiFe. For the top shield, most designs use permalloy (NiFe).
Shown in FIG. 1 is the basic structure used in the prior art. Seen there is magnetic bit sensor 11 resting on lower shield 12 and surrounded by side shield 13 and top shield 14.
As the sensor width shrinks into the nanometer range, HB encounters the following problems:
(1) The biasing field becomes so strong that movement of the free layer magnetization is constrained. The result of this is that the read back signal has low amplitude.
(2) The hard magnetic film cannot adequately shield the sensor from bits near to the bit that is being read.